The E. coli himA gene (38.5 minutes on the E. coli linkage map) encodes a protein involved in site-specific recombination. We find that the himA gene product is required for the precise excision of certain tranposons (e.g. Tn10) but not for others (e.g. IS1). The efficiency of transposition is not affected by a himA mutation. Analysis by 2-dimensional poly-acrylamide gel electrophoresis of proteins made by a lambda himA transducing phage suggests that himA is an 8,000 dalton MW protein.